Domino bit breaking

[WoodSam]

I'd appreciate information on the use of the Festool Domino. I am making some simple wine storage cases out of 5/8th inch fir plywood and was using the domino to join the various components and using the Domino plate from Ron to set the positioning of the dominos. The Domino size was 5 x 30 mm and the depth setting was 20mm for the end plunges and 12mm for the face plunges. The set up with the Domino plate was very simple and everything appeared to be going well until I attempted to join the pieces together and then I had trouble fitting the dominos in the slots and the boards were approximately 3mm apart. Further investigation revealed that the 5mm bit had broken at the tip and was about 3-4 mm short. I replaced the bit (fortunately I had the extra bit in the systainer/bit kit) and started redoing the domino slots. After about 80 slots the bit again broke at about 3-4 mm from the tip.

I am looking for advice as to why the bits broke.I suspect it has to do with my technique since it happened twice and I'd like to learn from my mistakes.

 

[ajones]

Hi thats odd what is your plunge rate?slow?  did you dig the broken part out of the work piece before reworking?

 

[grobin]

Had a problem with a bit getting very hot in high density ply.  Just went slower after sharpening the bit.  Apparently the bit didn't like the glue used.  I don't know what it was but the sales sleaze at the lumber yard said that it was better than any of the urea based glues and non toxic. 

 

[Tim Sproul]

Further investigation revealed that the 5mm bit had broken at the tip and was about 3-4 mm short.

I would send the bits back to Festool and see if there is a welding problem.  The bits are carbide tipped.

The other thing that might make the bits break is movement of the tool during the plunge action (either plunging into the work or exiting the work).  I also assume you are using dust extraction during machining.  The lack of dust extraction would make the bit run a lot hotter and the heat could damage the weld/bit.

 

[ThomasC]

I just had the same experience myself with the 5 mm bit - sheared off the tips of two of them. I was using it on 20 mm A-1 cabinet grade plywood (not the junk from HD that periodically has "metalic elements" in it). I'll be the first to admit that I'm somewhat new to the Domino, but it wasn't my first time either. I recently attended the Cabinet Construction class in Lebanon, and I was using the Domino exactly as we were taught. I was careful not to let the machine slip, and my feed-rate was steady - not too fast, not too slow. Ultimately I don't have a clear answer as to why this happened. Either opperator error, or possibly faulty welds on the bit. I'm not even sure if the tips of the bits are actually welded on, or if the bits are solid. After looking at all the bit sizes, the 5 mm looks like it is the most prone to breakage - even more than the 4 mm. The shaft on the 5 mm looks to be the longest in relation to it's diameter. This may make it a little more vulnerable, but who knows? Anyway, I just wanted to let you know that you're not the only person this has happened to. However, I don't have any explanation as to why it happed. Hopefully someone else will chime in on this.

TC

 

[WoodSam]

For further clarification, yes I was using dust extraction with the Domino and I am confidant that the Domino was not moving while plunging.Also there was no metal left in the slots from the initial bit breaking. It just seems strange to have two bits break in a very short time of usage. Also, it is intriguing that I am not the only one to experience this with the 5mm bit.

 

[mastercabman]

I have broke a couple 5mm bit before.It seems to me that it happen when you are plunging deeper than 15mm.Now,if i have to plunge deeper than 15mm,i go slow.I have not broken one since.

 

[JJ Wavra]

Like mastercabman said go slow.  I probably would not even plunge that deep with the 5mm bit.  If you think of it in terms of routing, though not exactly the same, it is like taking .25" bit and doing a 3/4" deep groove not recommended.  I think that the way the domino works helps with the dimension of the bits relative to the cut depth but you still have to be aware of what you are asking the bit to do.  I will sometimes just shorten the domino when you can not do half depth on both sides.
Jeff

 

[Rick Christopherson]

The bit cuts only with its tip. If you plunge in too fast, you force it to sweep sideways into uncut material. This will break the bit. It is very common for those with experience with biscuit joiners to assume Domino operates similarly, and therefore, plunge too fast.

The depth of the mortise has very little bearing on the stress on the bit. To use the router bit analogy that someone else mentioned, the Domino is in effect making hundreds of shallow sweeps/passes for the depth of the cut. The stress on the cutter is the same regardless whether it is a 1/8" depth or a 1" depth.

 

[WoodSam]

Thanks Rick for the guidance. It ties in very well since the broken part of the bit was embedded in the side of the slot. Lesson learned and I'll go slower when my replacement bits arrive.

 

[madera]

I also had a 5mm bit break doing 20mm holes. I was using imported  prefinished plywood. I just attributed it to it being junk in the board.